these are all side stories that testuya wanted to bring from the KH saga theres gooing to be one more KH game before the BIG ONE(KH3) birth by sleep was very close to being on the ps3 idk what happened though
I think i can answer that! the problem lies with the PS3 itself and doing multiple cross platform releases as the PS3 is horrible to code a game for, they most likely had a contract with Sony for a KH game but decided to make it for the PSP instead as thats simply cheaper.
Take a game like GTA4, that game was done on the Xbox in 2007 being completly ready for release but.. since Rockstar had a contract with Sony that stated that they could not release the game on the Xbox or PC before they released it on the PS3 they had to wait for the PS3 team to finish their product that ended up being pushed back an entire year because the game didnt work.
That could be one of the main reasons that your seeing it on the PSP.